In order to use charging columns with alternating current, wall charging stations or, if necessary, simple AC household receptacles for charging, the users of electric vehicles are dependent on on-board charging devices. This charging electronics is carried in the vehicle and must therefore be as small, light and inexpensive as possible. This requires extremely compact and efficient power electronic systems such as voltage converters.
The Fraunhofer Institute for Applied Solid State Physics IAF (Freiburg, Germany) has been researching monolithic integration in power electronics for years. With their latest research results, they combine current and temperature sensors, 600V power transistors with intrinsic flyback diodes and gate drivers in a GaN Power IC for the first time. As part of the GaNIAL research project, the researchers have demonstrated the functionality of all this functionality in a GaN Power IC and thus achieved a breakthrough in the integration density of power electronic systems.
Compared to conventional voltage converters, the new circuit not only enables higher switching frequencies and thus a higher power density, but at the same time fast and accurate condition monitoring directly in the chip. This is important because the increased switching frequency of GaN-based power electronics enables very compact designs, but also leads to stricter requirements with regard to monitoring and control. “Therefore, sensor technology integrated in the chip is a great advantage,” emphasizes Stefan Mönch, researcher in the field of power electronics at Fraunhofer IAF.
The integrated current sensor now enables the non-reactive measurement of the transistor current for control and short-circuit protection and saves space compared to conventional external current sensors. The integrated temperature sensor enables direct measurement of the temperature of the power transistor and thus maps this thermally critical point much more accurately and quickly than previous external sensors, since the distance and resulting temperature difference between sensor and measuring point is eliminated by the monolithic integration.
“The monolithically integrated GaN power electronics with sensor technology and control thus saves chip space, reduces the effort required for assembly technology and increases reliability. This is crucial for applications in which many small and efficient systems have to be installed in a small space, such as electromobility,” says Mönch, who designed the 4 x 3 mm² GaN chip.
For the monolithic integration, the research team uses the semiconductor material gallium nitride, which has been deposited on a silicon substrate (GaN-on-Si). The special feature of GaN-on-Si power electronics lies in the lateral nature of the material: The current flows parallel to the chip surface, whereby all connections are located on the top of the chip and connected via conductor paths. This lateral structure of the GaN components allows the monolithic integration of several components such as transistors, drivers, diodes and sensors on a single chip. A special property of gallium nitride is advantageous over other wide-bandgap semiconductors such as silicon carbide: GaN can be deposited on inexpensive and large-area silicon substrates and is therefore suitable for industrial use.